Russia - threadbanned users in OP

You are delving into the philosophical argument of the social construct and the obligations of the State to the Citizen... and the return obligations of the Citizen to the State. An example from the Pennsylvania Constitution of 1776, Art 8 is a fair case in point.

This is no recent argument. From an issue of Ethics and International Affairs in 2004.

Or from an 2010 issue of "Armed Forces and Society"

The latter seems to be the dominant line of thinking. Basically, it may be moral to refuse to serve in some circumstances, but if the fight is 'just' (and I would argue that your example of a peaceful Ireland being invaded by tanks coming South from Newry is about as 'just' as it gets), there is such a moral obligation.

Go to a 1936 issue (July) of International Journal of Ethics and you will find the following.

However, it also points out:

The question of the return duty of the citizen to the state has even made it to courts. In 1918, the draft law was challenged in the US Supreme Court.

The form of conscription which has proven a bit more troublesome on ethical grounds (but makes sense on practical) is peacetime conscription: If there is no active threat to the State, what right does the State have to compel service? The opinions seem a little more split on the matter. That is not, however, the current situation in Ukraine, and Putin may well be categorised as one of the "homicidal lunatics in control of government policy" referenced above.

With the acceptance that personal ethics are, of course, entirely personal, society inherently places limits on those individual foibles. (Ethical to kill certain people? To steal things? Whatever. They are our laws). To that extent, in modern society it seems likely that your position is an outlier and society may well demand your service regardless of your lack of feeling of personal obligation back to the State. Consider yourself fortunate that as an Irish resident, such a requirement is highly unlikely.

This is, of course, all a separate question of whether a country has the duty to return wayward citizens to the country of origin, which itself is rather untested in Europe. There was no extradition clause for draft dodging between the US and Canada in Vietnam. I am a little surprised that it has not yet been suggested by Ukraine, but it seems that the default position right now is "If you try to leave and we catch you, we'll punish you. If you make it out, we'll leave it be and consider things when we have less pressing matters to attend to".

I didn't only bring up US sources. To my knowledge, Hegel and Herzog were very much not American. The 1936 article was written by an Englishman named C. Delisle Burns, a Professor of Citizenship. (No idea if that's still a thing). The point is that it is a widely discussed concept, including in the US.

Well, Oxford defines society as "the aggregate of people living together in a more or less ordered community." The artificial construct in question has governed your activities for much of your life in the furtherance of that more or less ordered community, but you have a fair point: Let's assume there's a mass race for Rosslare. Unlike Ukraine where it's pretty easy to cross a border on foot, good luck swimming to Holyhead or Brest. You may well find yourself and your family stuck on the shore, awaiting a boat from... someone. I can't imagine Stena will be in a hurry to sail its ships to a war zone. What happens when, due to lack of resistance, the invading forces get to Rosslare, and you? Trust on the good offices of the invading force? That hasn't worked well for Ukrainian citizens who didn't get out from the areas Russia seized. Of course, this is all wildly hypothetical for the Irish situation.

As you do point out, Ireland is not the US. Neither is it Ukraine. Whatever the limited chances are of an invasion of Ireland, such was not the case for Ukraine, and the question is not in any way abstract. Ukraine was in the happy position that it did not need to take a defensive posture similar to, say, Norway, whose official stated goal for defense is not to defend the country per se as it would be an impossible task but simply to slow down the opposition long enough for help to arrive (Which is, in practice, pretty much the Irish position, although unstated). Ukraine, as a society, had the capability to defend itself, but only if that society also provided the mechanism to do it. Much as any society can compel certain actions of its citizens (you do pay tax and generally obey the laws, right?) on the grounds that the citizenry as a general whole believe that it is communally beneficial to do that, it seems logical that those actions can compel military service as well. By inherent definition, 'compel' means forcing a course of action no matter the personal opinions of the person in question.